Hi Bill,
The kit comes molded in green styrene plastic but everything needs to be painted.
Thomas,
The tracks could be controlled individually, just like a modern bulldozer so the only thing I can figure is with all the weight forward of the tracks the machine would be nose heavy therefore needing support up front. This is where the wheel comes into play. Even with the tracks being able to move the machine from left to right a steerable wheel was needed to get the front end where it needed to go. Watching videos on you tube shows the operator steering the wheel as the tractor moves.